On-demand portable chlorine dioxide generator

ABSTRACT

An on-demand portable chlorine dioxide generator has a reagent bound medium in a first enclosed volume; a complementary reagent solution in a second enclosed volume, and a structure for selecting between a first position where the complementary reagent solution is forced through the reagent bound medium and a second position where said complementary reagent solution remains isolated from the reagent bound ion exchange medium, where a ClO 2  solution is generated only during periods when the structure for forcing is actuated. The ClO 2  solution can be discharged for use as a portable sprayer that can be used to treat surfaces infected by anthrax or other biological contaminants. When the bound reagent is chlorite, the complementary reagent is an acid or an oxidant. When the bound reagent is an acid or an oxidant, the complementary reagent solution is a chlorite solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/095,388, filed May 29, 2008, now U.S. Pat. No. 7,964,138, whichis the U.S. national stage application of International PatentApplication No. PCT/US2006/061335, filed Nov. 29, 2006, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 60/780,257,filed Mar. 8, 2006, and U.S. Provisional Patent Application Ser. No.60/740,393, filed Nov. 29, 2005, the disclosures of which areincorporated by reference herein in their entireties, including anyfigures, tables, or drawings.

FIELD OF THE INVENTION

The invention relates to on-demand chlorine dioxide generators.

BACKGROUND

The use of certain gases as sterilizing agents as bactericides,viricides and sporicides, is known. Chlorine dioxide (ClO₂) is one suchagent and is used annually in the U.S. at a rate of approximately 4million pounds per year, primarily for water purification as areplacement for chlorine/hypochlorite (bleach). Chlorine dioxide is aneffective microbicide as a gas and in solution and also can destroycertain chemical substances and toxins. For example, U.S. Pat. Nos.4,504,442 and 4,681,739 to Rosenblatt et al. disclose the use ofchlorine dioxide gas as a chemosterilizing agent.

In addition, chlorine dioxide has excellent environmental qualities, asit does not produce large quantities of chlorinated hydrocarbonbyproducts. Although large-scale production of chlorine dioxide ishandled effectively by chemical generator systems, typically being truckmounted when portability is needed, small-scale production is morechallenging. In particular, on-demand production, rapid deployment, andportability for use in personal protection are difficult to combine in asingle product.

Many processes are known for the production of ClO₂ in gas or solutionforms suitable for large-scale use. Success in the use of ClO₂ fordomestic anthrax clean-up has amply demonstrated this point for caseswhere a significant amount of time is available to transport heavyequipment and chemicals to the contamination site. Usually, thesophisticated equipment needed to produce ClO₂ requires ample power,particularly if electrolysis is used for generation.

On the other hand, portable ClO₂ dispensers for immediatedecontamination that could be carried by a person and used in smallareas (offices, labs, clinics, etc) or transported on vehicles are notgenerally available. A viable working requirement is that the dispensershould be the size and function that can be easily handled by a singleindividual. For example the dispenser can have the form of and functionsimilarly to a typical fire extinguisher and preferably would require noexternal power and work by simply opening a valve to release adecontaminant fluid with essentially no time delay. A reasonable targetis the production of 1 L of decontaminant fluid with greater than 5 mMClO₂ in less than 1 minute for such a portable dispenser. Furthermore,larger devices that could be portable by vehicle or dolly could alsoprovide for immediate decontamination over larger areas, and smalldevices could provide personal decontamination of remote water supplies.

Moreover, chlorine dioxide solutions (chlorous oxide) in any form arehighly unstable, so it is necessary to generate the solution immediatelybefore use. Accordingly, the reaction components which when mixedtogether produce chlorine dioxide gas must be maintained separatelyuntil gas production is desired.

In general, chlorine dioxide solutions can be produced by treatment ofchlorite salt solutions (e.g. NaClO₂) with an acid solution to produceacidic solutions that contain ClO₂. The ClO₂ can be used in thesesolutions or flushed as a gas into water to produce aqueous ClO₂. It isdifficult to use this traditional approach to design, for example, aportable sprayer that can be used to treat surfaces infected by anthraxor other biological contaminants.

U.S. Patent Application Publication Nos. 20040241065 and 2004062680 toKampa disclose on-demand chlorine dioxide generators, which can beportable. Kampa discloses a chlorine dioxide gas generating kitincluding a gas generating apparatus having a first reaction componentcontained therein and a second reaction component contained therein. Thefirst and second reaction components are separated within the apparatusby at least one rupturable membrane. To activate the apparatus, themembrane is ruptured to permit contact between the first and secondreaction components to facilitate a chemical reaction therebetween,which produces the chlorine dioxide gas.

The reaction components disclosed by Kampa are both liquid reagents.Liquid reagents risk leakage and require relatively large storagevolumes. Moreover, chlorine dioxide production according to Kamparequires the rupture a rupturable membrane to permit contact between thereagents. Rupture of the membrane can occur inadvertently duringhandling or even prevent dispensing when desired. Significantly, therequired rupture provides only one-shot use where the entire firstreaction component is mixed with the entire second reaction componentupon rupture of the membrane.

Ion exchange mediums are known for the formation of chlorous oxide. Forexample, U.S. Pat. No. 3,684,437 to Callerame discloses production ofchlorous oxide by ion exchange between a mixed bead cation-anionexchange resin and a chlorite of an alkali metal or an alkaline earthmetal with a flow rate of 1 mL/minute or less. Heating the solutionformed by the ion exchange reaction liberates gaseous chlorine dioxide.Similarly, U.S. Patent Application Publication Nos. 20030064018 and20050196337, both to Sampson et al., disclose generation of chlorousacid from a chlorite salt precursor, a chlorate salt precursor, or acombination of both by passing an aqueous solution of the precursorthrough a cationic ion exchange resin in a hydrogen ion form and acatalytic material to accelerate the decomposition of chlorous acid tochlorine dioxide using gravity feed and a flow rate of 30 mL/minute.Both Callerame and Sampson disclose only bulk or laboratory methods forforming chlorous oxide, with no adaptability for on-demand or portablechlorous oxide generation, where flow rates of approximately 1 L/minuteor more are needed.

SUMMARY OF THE INVENTION

An on-demand ClO₂ generator includes a reagent bound medium in a firstenclosed volume; a complementary reagent solution isolated from thereagent bound medium in a second enclosed volume; a structure forselecting between a first position where the complementary reagentsolution is forced through the reagent bound medium and a secondposition where the complementary reagent solution remains isolated fromthe reagent bound medium, where ClO₂ (aq) is generated only duringperiods when the structure for forcing is actuated, and; an outletthrough which a ClO₂ or a solution capable of spontaneously forming ClO₂is discharged. The first and the second enclosed volumes can be within asingle common container and the structure for forcing can be apressure-actuated source such as a plunger, a pump, or a compress gaswith one or more valves. The structure for forcing can include acheck-valve or break-seal situated between the first and second volumeswhere the check-valve or break-seal permits flow upon actuating thestructure for forcing the complementary reactant solution through thereactant bound medium. The generator can also include a basic or mixedbead ion exchange medium disposed downstream of the reagent bound ionexchange medium, to result in a near neutral or salt free ClO₂ solutionsare discharged. The outlet can be a spray nozzle or a structure forgenerating an aerosol.

The reagent bound medium can be an acidic ion exchange resin and thecomplementary reagent solution is a chlorite solution. The reagent boundmedium can be an oxidant bound medium and the complementary reagentsolution can be a chlorite solution. The oxidant bound medium is a metalcomplex bound to a medium. The metal complex can be an iron complex. Theoxidant bound medium can be a Br₃ ⁻ bound ion exchange resin. Thereagent bound medium can be a chlorite bound ion exchange medium and thecomplementary reagent solution can be an acid solution. The acidsolution can be an aqueous buffer solution of pH of about 3.5 to about 5with a buffer capacity of about 2 to about 5. The reagent bound mediumcan be a chlorite bound ion exchange medium and the complementaryreagent solution can be an oxidant solution, such as aqueous bromine orchlorine. The oxidant solution can be generated upon forcing a saltsolution in a portion of the second volume through an oxidant boundmedium in a second portion of the second volume situated immediatelyadjacent to the chlorite bound ion exchange medium in the first volumewhen the structure for forcing is actuated. The oxidant bound ionexchange medium can be a tribromide bound ion exchange medium.

A method of generating ClO₂, comprising the steps of: providing areagent bound medium and a complementary reagent solution isolated fromone another, and switching between a position for forcing thecomplementary reagent solution through the reagent bound medium and asecond position where the complementary reagent solution remainsisolated from the reagent bound ion exchange medium, wherein ClO₂ (aq)is generated only during periods when a structure for forcing isactuated. The reagent bound medium can be an acidic ion exchange mediumand the complementary reagent solution can be a chlorite solution. Thereagent bound medium can be a chlorite bound ion exchange medium and thecomplementary reagent solution can be an acid solution. The reagentbound medium can be an oxidant bound ion exchange medium and thecomplementary reagent solution can be a chlorite solution. The reagentbound medium can be a chlorite bound ion exchange medium and thecomplementary reagent solution can be an oxidant solution.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings, embodiments that are presentlypreferred, it being understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

FIG. 1 shows a cross-section of a prototype on-demand chlorine dioxidesprayer according to an embodiment of the invention using a compressedgas for forcing.

FIG. 2 shows a cross-section of an embodiment of the invention where thegenerator is in the form of a syringe.

FIG. 3 shows a representation of an oxidant bound resin wherein an Fe⁺³oxidizer is bound to the resin via electrostatic attraction to ananionic resin.

FIG. 4 shows a representation of an oxidant bound resin wherein an Fe⁺³oxidizer is bound to the resin via a bidentate ligand bound the resinaccording to another embodiment of the invention.

FIG. 5 shows a representation of an oxidant bound resin wherein a Br₃ ⁻oxidizer is bound to the resin via electrostatic attraction to acationic resin.

FIG. 6 shows a representation of a chlorite bound ion exchange resinaccording to another embodiment of the invention.

FIG. 7 shows a cross-section of a prototype on-demand chlorine dioxidesprayer 101 according to an embodiment of the invention comprising twoseparate containers coupled by a coupling 105 using a compressed gas 13for forcing a complementary reactant solution 6 from a second container108 into a reactant medium 2 in a first container 104 when the valve 10is opened to allow discharge of the ClO₂ solution formed by reaction.

FIG. 8 shows a cross-section of a prototype on-demand chlorine dioxidesprayer 201 according to an embodiment of the invention comprising threeseparate containers coupled by couplings 205 and 215 using a compressedgas 13 from a compressed gas container 213 for forcing a complementaryreactant solution 6 from a second container 108 into a reactant medium 2in a first container 204 when the valves 10 and 210 are opened to allowdischarge of the ClO₂ solution formed by reaction.

DETAILED DESCRIPTION

An on-demand chlorine dioxide (ClO₂) generator 1 is illustrated in FIG.1 and comprises a reactant bound medium 2 in a first enclosed volume 4,and a complementary reactant solution 6 in a second enclosed volume 8isolated from the reactant medium 2. A structure 10 for selectingbetween a first position where said solution 6 is forced through saidreactant bound medium 2 and a second position where said solution 6remains isolated from said reactant medium 2 is provided, wherein ClO₂(aq) is generated only during periods when said structure 10 for forcingis actuated resulting in the discharge of a ClO₂ containing solutionthrough an outlet 12. As shown in FIG. 1, the structure for forcingincludes a valve 10 which is shown in the second position for isolationand is actuated by rotating one quarter turn counterclockwise to theforcing position. In a preferred embodiment of the invention, the firstand second enclosed volumes are themselves enclosed within a singlecommon container.

Although the complementary reactant solution 6 is generally describedherein as being directly incorporated into the generator 1, thiscomplementary reactant solution 6 can be formed within the generator,where the reactant is stored as a solid or gas to enhance the shelf lifeof the generator under adverse storage conditions and including thesolvent (e.g. water) in a third enclosed volume to generate the solutionupon actuation of the structure for forcing to force the solvent intothe reactant forming the solution immediately prior to its forcing intothe ion exchange medium. It is preferable that all enclosed volumes areenclosed in a single common container although two or more containersthat can be readily coupled are within the scope of the invention.

The invention provides for the convenient and efficient production ofchlorine dioxide on-demand and in controlled amounts. Unlike one-shotdevices based on membrane rupture of Kampa, devices according to theinvention can dispense ClO₂ (aq) on-demand over multiple separateintervals of time, and can be configured to be refillable. Moreover, theinvention can be easily adapted for portability

In addition, although chlorine dioxide (ClO₂) generation using a solidmedium is known, the invention represents the first portable on-demandchlorine dioxide (ClO₂) generator device using a solid medium. Althoughthe ClO₂ (aq) product is highly corrosive, the Inventors haveunexpectedly found that devices according to the invention operatereliably with standard fittings and no special storage protocol.Moreover, pressurization has surprisingly been found to producereliable, significant and continuous ClO₂ (aq) product flow. As notedabove, Sampson teaches gravity feed. The generator of this invention isdesigned to have a flow rate that delivers approximately 1 L of solutionin less than 2 minute or even less than 1 minute. Furthermore the ClO₂in solution will be present at a concentration of between 2 μM to 100mM, and preferably from 1 mM to 50 mM to assure efficacy and safety.

The generator can be of different sizes and styles depending upon thenature of its use and the environment in which it is to be used. Forexample, as shown in FIG. 2, a very small generator can be a syringestyled unit 14 where the structure for forcing is a plunger 16 that isactuated manually by depression of the plunger 16 in to a syringe bodyto force the complementary regent solution 18 through a reagent boundmedium 20 near the outlet 21 of the syringe 14. Such a generator may beused by soldiers or outdoorsman for water purification or othermicrobial decontamination in a remote environment. Such a syringe can beassembled immediately prior to use with a medium 20 and a solution 18placed in the syringe generator immediately prior to use and storedseparately. A pressurized apparatus can have the general appearance of acommon hand held or cart mounted fire extinguisher as shown in FIG. 1.In this case a single container where a reagent bound medium 2 in onevolume 4 is separated from a complementary reagent solution 6 in asecond volume 8 where the apparatus is under a gas pressure 13 such thatwhen, for example, a valve 10 is actuated the solution 6 under pressureis forced through the reagent bound medium 2 and discharged throughoutlet 12 into a fluid, onto a surface, or into the air to liberate asolution and the ClO₂ contained therein. In general, a check valve 7 isalso included between the two volumes 4 and 8 as part of the structurefor selecting between forcing and isolation. The pressure may be from acompressed gas 13 contained within the generator 1 or alternatelysupplied to the container from an attached gas canister. A pump may beused to supply a gas pressure needed for forcing the complementaryreagent solution through the reagent bound medium. A liquid pump, suchas a syringe, diaphragm, or peristaltic pump, may be used for forcingthe solution through the medium. Pumps may be manually driven ormechanically driven with an available fixed power supply or a portablepower supply such as a battery. The invention is not limited withrespect to size, shape and modes of transport so long as the generatoris portable. One of ordinary skill in the art can easily envision otherstructures for containment, actuation, and mobility.

The outlet for the discharge can be of a design such that a stream, aspray, or an aerosol of ClO₂ solution is discharged. For example, whenpurifying water a stream is generally sufficient to contact the ClO₂solution and water, while the decontamination of a surface may be betterserved by a solution passing through a nozzle to give a fan or conicalshaped spray. The formation of an aerosol at the point of discharge maybe better suited for the decontamination of an enclosed space, such as aroom, where the very high surface area of an aerosol can permit therapid separation of the ClO₂ gas into the atmosphere which can diffusethrough the relatively large volume of the room and decontaminate allsurfaces including airborne particulates. Outlets, which are capable ofgenerating an aerosol, are well known.

Although the invention is generally described herein as a chlorinedioxide generator, the scope of the invention is far broader. Moregenerally, the invention relates to rapid and controlled generation oflow stability solutions of an acidic, basic or near-neutral nature frominert salt precursor solutions using ion exchange resins or othermodified solid supports. Thus, chlorine dioxide is one of many possibleunstable reactive reagents that can be produced from stable precursorsby this technology. For example, bromine dioxide can be generated viathis technology.

The complementary reactant solution as described in the embodiments ofthe invention is an aqueous solution. However, it is within the scope ofthe invention to use solvents other than water and to use mixedsolvents. The solvent can be various alcohols, glycols, ketones,aldehydes, ethers, amines, and even hydrocarbons. The solvent can be acombination of such organic chemicals and water in any proportions.Optionally, the solution can also include a surfactant. The surfactantcan be ionic or non-ionic. The surfactant can be included to affect theefficiency of the reaction within the generator or used to enhance theeffectiveness of the resulting ClO₂ solution at decontaminatingsurfaces.

The invention is based on a solid medium to which a reagent for theformation of chlorous acid or chlorine dioxide is bound. Such a mediumcan be clay, a silicate, an organic polymer, carbon or other structureonto which a reagent can be immobilized. In particular, polymericresins, such as ion exchange resins and modified polymeric resins arepreferred. Resins can be in the form of beads, pellets, or films. Usefulpolymeric resins include cross-linked polystyrenes, polyacrylates, orpolymethacrylates which contain repeating units containing functionalgroups to bind a reagent. The functional groups for binding can includeions or ligands. The ions can be either cations or anions and act as acounterion to an anionic or cationic reagent, respectively. Theseligands can be mono- bi- or polydentate. A ligand is one that is capableof forming a strong complex to a reagent such as a metal cation in arelatively high oxidation state.

For example, in one embodiment, a solid ion exchange medium can be inthe form of an acidic ion exchange resin, the resin being functionalizedto exchange hydrogen ions, H⁺, for other cations in solutions (e.g.Dowex™ from Dow Chemical). This allows the convenience of passing achlorite solution through the resin bed of the acid, thus convertingchlorite to HClO₂ and leading to the rapid formation of ClO₂ (aq) as thesolution emerges from the resin bed. Additionally, a basic mixed bead(acidic and basic) ion exchange resin, 3 of FIG. 1, may be used with theacidic ion exchange resin to permit discharge of a neutral stream ofClO₂ solution.

In reference to FIG. 1, the passage of a NaClO₂ solution 6 through anacidic ion exchange resin 2 forms a chlorine dioxide solution accordingto an embodiment of the invention. Na⁺ exchanges with H⁺ to produceHClO₂, which rapidly decomposes according to Equation 1.5HClO₂→4ClO₂+HCl+2H₂O  Equation 1

The flow of the chlorite solution 6 into the solid acid resin 2 providesfor intimate mixing of the acid with the chlorite in solution. Thus,there is no need for shaking or stirring as required by the Kampasystem. An optional basic or mixed bead ion exchange resin 3 is alsoshown in FIG. 1. The resin 3 can neutralize the HCl byproduct generatedby the reaction of Equation 1 above. Performing the two steps describedabove using traditional methods would require mixing three solutions insequence, which is not easily accomplished in a single unit device.

The solid ion exchange resin provides several advantages over aconventional liquid acid source. The flow of the NaClO₂ solution throughthe resin bed provides for essentially instantaneous mixing of thereactants (H⁺ and ClO₂ ⁻). In addition, the solid resin is notcorrosive, storage is easy, and the resin is highly chemically stablewhile dry.

Appropriately sized resin particles (such as used in water filtrationsystems, for example) can be used for the ion exchange resin. Typicallythese particles are spheres on the order of 500 microns, but can havedifferent shapes or sizes, provided that liquid flow is possible at anacceptable rate.

In a preferred embodiment of the invention, the solid ion exchangemedium can be in the form of an oxidant resin. An “oxidant resin” asdefined herein is generally a material, composed of chemically modifiedpolymer beads or the like, to which an oxidant agent (Ox) has beenattached. Such a resin can be prepared by any number of methods in whichoxidants are attached to a solid support that allows the ready flow ofliquid through a column or other container packed with the support. TheOx can be selected from any variety of compounds, such as metalcoordination complexes, and is generally referred to as “one electronoxidant.” These are molecules that have the property of accepting oneelectron in chemical reactions. Other non-metallic oxidants can be used.

As the chlorite solution passes through the oxidant resin, the Oxaccepts an electron thus oxidizing the chlorite anion to ClO₂ as shownby Equation 2 below. A resin for this embodiment can be prepared byattaching an iron complex as the Ox to a resin. One exemplary oxidantresin is a cation ion exchange resin (Dowex) which has been treated withan aqueous solution of Fe(phenanthroline)₃ ⁺² to yield a resin withstrongly electrostatically bound Fe⁺² ions followed by oxidation of theFe⁺² to Fe⁺³ upon contacting with an oxidant such as bromine water. ThisFe⁺³ modified resin, is illustrated in FIG. 3, where a resin bead 25with covalently bound phenylsulfonate anions 27 immobilizeFe(phenanthroline)₃ ⁺³ cations 26. Other anions, such as carboxylates,can be covalently bound to the resin and are in the scope of theinvention. Additional anions are necessarily present to maintain theneutrality of the resin; these anions are not shown and will be otherphenylsulfonate anions attached to the resin and/or free anions insolution. Any additional free anions within the resin's influence canhave various valences, for example they can be monovalent or divalent,and their use is within the scope of the invention. The resin can beused to produce chlorine dioxide from chlorite according to the reactionabove by passing a chlorite solution over the resin. This resin form ofan oxidant reactant has a high surface area of the redox agent becauseof the large effective surface of the resin, which promotes a high yieldof ClO₂. The oxidant resin can be made to be very stable during storageby choosing an appropriate oxidant and packing the resin in thegenerator in a dry form. This embodiment can also provide a near neutralpH (in the range of 5 to 9) to an eluting ClO₂ solution compared to theClO₂ solutions produced using an acid ion exchange resin according tothe invention, and thus the performance of a downstream neutralizationstep is not required to yield a near neutral pH ClO₂ solution whenneeded.ClO₂ ⁻+Resin-Ox→ClO₂+Resin-Ox⁻  Equation 2

One variation of the oxidant bound resin is that where the resincontains a bound bidentate ligand such as a bound phenanthroline, asshown in FIG. 4, or bipyridine unit which can bind to a ferric ion orother oxidized metal ion capable of oxidizing chlorite ion to chlorinedioxide rather than being electrostatically bound as an exchangeable ionpair comprising a metal ion and an anionic site of the resin. Forexample, the resin portion of Resin-Ox of Equation 2 above can be apolystyrene resin bead 30 with attached phenanthroline ligand 32 and theOx portion of Resin-Ox can be Fe(phenanthroline)₂ ⁺³ 34. Upon reactionof this bound oxidant with sodium chlorite solution, the effluent can bea stream of ClO₂ in water with the Ox⁻ portion of the co-producedRein-Ox⁻ in Equation 2 is Fe(phenanthroline)₂ ⁺²Na⁺. A mixed bead ionexchange resin, such as that commonly used for water purification, canbe used downstream of the oxidant bound resin to assure a salt freeaqueous solution of ClO₂. The advantage of such a system is theextremely high rates of reaction possible with such a resin. Forexample, where in the case using a resin bound Fe(phenanthroline)₂ ⁺³, arate constant of about 2×10⁷ M⁻¹s⁻¹ allows for on demand conversion of achlorite solution to a chlorine dioxide solution.

A third variation for the Resin-Ox of Equation 2 is Br₃ ⁻ bound to anion exchange resin. Such a resin can be prepared by passing a brominewater solution through an anionic exchange resin with bound Br⁻ ions.For example, an Amberlite™ anion exchange or resin in the OH⁻ form wasconverted to the Cl⁻ form with dilute hydrochloric acid and then to theBr⁻ form using NaBr. All free Cl⁻ and Br⁻ ions were washed from theresin with deionized water. Saturated aqueous bromine at 0.20 M wasdiluted to 10 mM and slowly rinsed through the column until the resinwas dark red with significant amounts of Br₂ in the effluent. The resinwas then washed with water until the Br₂ content of the effluent was ata minimum. The tribromide resins, illustrated in FIG. 5, are stable inthe dry and wet forms without significant loss of Br₂. FIG. 5 shows theresin bead 36 with covalently bound pendant trialkylamonium cations 37electrostatically binding the Br₃ ⁻ 38 anionic oxidant. In the presenceof chlorite ion from a sodium chlorite solution, the equilibrium can beshifted to liberate Br₂, which converts two equivalents of ClO₂ ⁻ toClO₂ with the formation of two bromide ions. A mixed bed ion exchangeresin can be used to scavenge NaBr from the effluent, allowing thedischarge of a salt free aqueous ClO₂ solution.

Another embodiment of the invention is based on a solid ion exchangemedium upon which a chlorite ion is bound to the resin, as illustratedin FIG. 6. For example, the solid ion exchange medium can be prepared byexchanging chlorite ions in solutions, with an anion exchange resincommonly used in water treatment (e.g. Amberlite IRA 400™). These anionexchange resins 40 typically have covalently bound tetraalkylammoniumions 42 and are available with hydroxide or other anions, such aschloride, bound to the resin. The exposure of a soluble chlorite salt tothe anion exchange resin, typically by passing the chlorite saltsolution through a column of the resin, results in a chlorite 44 boundresin via the electrostatic attractions of the ion pair. This resin maybe used in the wet state or a dry state.

The chlorite bound resin allows the passing of a mobile phasecomplementary reagent 6 comprising an aqueous solution of an acidthrough the chlorite bound resin bed 2, thus converting chlorite toHClO₂ and leading to the formation of ClO₂ (aq) as the solution emergesfrom the resin bed at outlet 12 as shown in FIG. 1. Equation 3, below,gives the reaction of the chlorite bound resin with an aqueous acidsolution. Resin-ClO₂ ⁻ represents the covalently boundtetraalkylammonium chlorite sites of the resin. The anion attached afterexchange and reaction is given as X⁻ but, for example, can be CF wherethe HX exchanging with the resin is HCl. The rate of ClO₂ generationdepends upon the pH of the acid solution. However, the use of a buffersolution as the aqueous acid solution can permit rapid formation of ClO₂(aq) at pH buffers as high as about 5 such that a strong acid solutionis not required. Weak acids, such as acetic acid and related organiccarboxylic acids, are preferred but other organic acids, includingorganophosphoric and sulfonic acids, can be used. Mineral acids, such ashydrochloric and sulfuric acid, can also be adapted for use. Buffersolutions will typically be weak acid-conjugate base pairs, for example,acetic acid-sodium acetate solutions, with a buffer capacity of about 2to about 5.5Resin-ClO₂ ⁻+5HX→5Resin-X⁻+2H₂O+HCl+4ClO₂  Equation 3

In yet another alternate embodiment, an oxidant can be included as thecomplimentary reactant in solution rather than an acid. The oxidant uponexposure to the chlorite bound resin can either directly oxidize resinbound chlorite with a neutral oxidant or oxidize chlorite that isexchanged off the resin with anions in the solution. The directoxidation of resin bound chlorite has a significant kinetic requirement.In this case the redox reaction, Equation 4, must have a high rateconstant to assure that significant conversion of chlorite to ClO₂occurs in the bed, as the precursor solution can pass through the resinat a typical flow rate of about 10 to about 20 mL per second through a 2cm diameter bed. This is a flow rate that is required to deliverapproximately 1 L of solution in less than 2 minute to less than 1minute.Resin-ClO₂ ⁻+Ox→ClO₂+Resin-Ox⁻  Equation 4

Some oxidants that have very high rate constants including ionic metalcomplexes and neutral molecules such as Br₂ as indicated above for resinbound oxidants. For example, dry chlorite resin can be incorporated intoa cartridge in a pressurized or pump operated spray device with anoxidant contained in a solution. Upon activating the sprayer, thesolution passes through the resin bed and the ClO₂ forming reactionoccurs, producing an effluent with strong oxidative and biocidalproperties.

Oxidation of the chlorite ion exchanged from the resin permits sloweroxidants and permits a wider choice of oxidants, since the ClO₂production can occur in the effluent itself on a time scale of secondsto minutes. There are many oxidants that can be used to produce ClO₂ inthe effluent. In addition, the operating pH range can be set using abuffer to a wide range of values from acidic to basic, with the specificpH range depending on the oxidant used.

Examples of oxidants that may be used include main group compounds suchas chlorine, bromine, peroxides, and various related main groupoxidants. Another class of oxidant that can be used is metal complexes,such as Fe(phenanthroline)₃ ⁺³, which have very high one-electronreaction rates with chlorite. Other metal oxidants can carry out thegeneration of ClO₂ as given in Equation 4, above, but require acidicmedia to do so.

For example, 15 mL of chlorite-bound Amberlite exchange resin wastreated repeatedly with bromine water (40 mL at a concentration of <10mM). The effluent contained ClO₂ at the expected concentrations, and allthe bromine was consumed when excess chlorite was available in theresin. The pH of a bromine water solution is between 3-4 due to the HOBrpresent at equilibrium. In this case, the reaction occurs in the resinbed itself and ClO₂ is produced immediately in the effluent solution.The pH of the product solution can be raised prior to dispersal by useof a second ion exchange resin cartridge incorporating a weak base suchas bicarbonate, acetate or phosphate, a strong base such as hydroxide ora mixed bead. Commercially available weak base ion exchange resins basedon resin bound tertiary amines can potentially react with the ClO₂produced from the chlorite bound resin. Although these tertiary amineresins are not preferred for use in an apparatus where the parts are tobe recycled and the resins are to be regenerated since resin degradationcan occur upon standing after a discharge, the rate of amine oxidationis typically not significant with respect to the rate of ClO₂ generationin and dispensing from the device and, therefore, can be used in anembodiment of the invention.

When a volatile oxidant, such as bromine and chlorine, and volatileliquids are used in the practice of the invention, a check valve orbreakseal is best included between the first volume and second volume aspart of the structure for forcing to avoid diffusion of the gas or flowof liquids into the chlorite resin prior to the desired actuation anddischarge. An alternate to storage of the volatile oxidant is to fix theoxidizer to a resin. For example, bromine reacts with bromide ions andis bound to an anionic exchange resin as Br₃ ⁻ ions. The Br₃ ⁻ ions isreleased from the resin by forcing a salt solution, for example aqueousNaBr, through the tribromide bound resin and subsequently passing theformed Br₃ ⁻ solution through the chlorite bound resin upon switchingthe actuator into the forcing position. The Br₃ ⁻ ion released by ionexchange with the salt is the oxidant in this embodiment.

The solid resin design according to the invention allows ClO₂ to begenerated in a flow process that is readily adaptable to portablegenerators. FIG. 1 shows a prototype on-demand chlorine dioxide sprayeraccording to the invention, which resembles a conventional fireextinguisher in physical appearance. The spray device 1 provides both areagent bound medium 2 and a basic ion exchange resin 3, and acomplementary reagent solution 6. Spray device 1 includes an outlet 12that can have a spray nozzle including spray valve 10. The resin 2 isisolated from the complementary reagent solution 6 by a conventionalone-way flow or check valve 7 until it is time to dispense the solution.Pressurization or other standard techniques can be used to force thesolution 6 through the resin 2 before it exits the sprayer as a ClO₂solution upon actuating a valve 10. Although generally not preferred, aburstable membrane actuated by a pressure differential can be used toinduce flow through the ion exchange medium.

The ClO₂ concentration, flow rate, physical properties, and the pH ofthe dispensed solution can be controlled by selection of thecomplementary reagent concentration in solution, the volume of reagentbound resin, pressures, and the inclusion of certain additives (e.g.acids, bases, salts, detergents and surfactants). Additives such asdetergents and surfactants can improve the efficacy of the solutionsproduced and increase the activity of the oxidizing process by morerapidly wetting a dry resin.

The invention can be used to produce portable chlorine dioxidegenerators that have a long shelf life (e.g. several years) becausereactive components are separated from one another. The use of solidreagent bound resin makes the two-reactant generator as simple to use asa single liquid sprayer, such as a fire extinguisher. The invention canbe used to generate ClO₂ for many purposes including decontamination ofsurfaces, water purification, bio-medical sterilization, as well asdecontamination of bio-terrorism and chemical agents.

There is a variety of applications for the invention as it is aconvenient and reliable ClO₂ generator method. Military and homelandsecurity uses are numerous for treating anthrax, other bioagents, andcertain chemical agents. The military is presently searching for areplacement decontamination solution for use in portable sprayers forvehicle and ships. Water purification for camping and military use isalso a potential application. Medical sterilization is another expecteduse of the invention. A portable ClO₂ device can also be used by firstresponders to suspected attacks in offices, buildings, subways and othersites.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, theforegoing description is intended to illustrate and not limit the scopeof the invention. Other aspects, advantages and modifications within thescope of the invention will be apparent to those skilled in the art towhich the invention pertains.

1. An on-demand ClO₂ generator, comprising: a solid reagent bound mediumin a first container, said first container having an inlet and an outletfor discharging a ClO₂ solution; a complementary reagent solution in asecond container separate from said first container, wherein said firstcontainer and said second container are coupled, wherein said secondcontainer is situated upstream of said first container, and wherein thecomplementary reagent solution is stored in isolation of said solidreagent bound medium until generation of said ClO₂ solution is demanded;a pressure source situated upstream of said complementary reagentsolution; and at least two valves for selecting between a first positionfor storage, wherein said solid reagent bound medium in said firstcontainer is isolated from said complementary reagent solution in saidsecond container, and a second position for demanding, wherein saidcomplementary reagent solution from said second container is forcedunder pressure through said inlet and through said reagent bound mediumin said first container, and wherein said ClO₂ solution is generated anddischarged through said outlet only during periods when said at leasttwo valves are in said second position, wherein said at least two valvescomprise a first valve situated between said first container and saidsecond container and a second valve situated at said outlet of saidfirst container.
 2. The ClO₂ generator of claim 1, further comprising abasic or mixed bead ion exchange medium, within said first containersaid basic or mixed bead ion exchange medium being situated between saidreagent bound medium and said outlet, wherein said ClO₂ solutiondischarged through said outlet is near neutral in pH or salt free. 3.The ClO₂ generator of claim 1, wherein said pressure source comprises aplunger, a pump, or a compressed gas in said second container.
 4. TheClO₂ generator of claim 1, wherein said pressure source comprises acompressed gas in a third container coupled to said second containerwherein said third container is separate from said second container andsaid first container.
 5. The ClO₂ generator of claim 1, wherein said atleast one valve comprises at least two valves.
 6. The ClO₂ generator ofclaim 1, wherein said outlet further comprises a nozzle.
 7. The ClO₂generator of claim 1, wherein said complementary reagent solutioncontains a surfactant.
 8. The ClO₂ generator of claim 1, wherein saidreagent bound medium comprises an acidic ion exchange resin and saidcomplementary reagent solution comprises a chlorite solution.
 9. TheClO₂ generator of claim 1, wherein said reagent bound medium comprisesan oxidant bound medium and the complementary reagent solution comprisesa chlorite solution.
 10. The ClO₂ generator of claim 9, wherein saidoxidant bound medium comprises a metal complex bound medium.
 11. TheClO₂ generator of claim 10, wherein said metal complex comprises aferric salt complex.
 12. The ClO₂ generator of claim 9, wherein saidoxidant bound medium comprises a main group oxidant bound ion exchangeresin.
 13. The ClO₂ generator of claim 12, wherein said main groupoxidant bound medium comprises a Br₃ ⁻ bound ion exchange resin.
 14. TheClO₂ generator of claim 1, wherein said reagent bound medium comprises achlorite bound ion exchange medium and said complementary reagentsolution comprises an acid solution.
 15. The ClO₂ generator of claim 14,wherein said acid solution comprises an aqueous buffer solution of pH ofabout 3.5 to about 5 with a buffer capacity of about 2 to about
 5. 16.The ClO₂ generator of claim 1, wherein said reagent bound mediumcomprises a chlorite bound ion exchange medium and said complementaryreagent solution comprises an oxidant solution.
 17. The ClO₂ generatorof claim 16, wherein said oxidant solution comprises aqueous bromine orchlorine.
 18. The ClO₂ generator of claim 16, wherein said oxidantsolution is generated upon forcing a salt solution from said secondcontainer through an oxidant bound medium in a second portion of saidfirst container situated immediately adjacent to said chlorite bound ionexchange medium in said first container when said at least one valve forselecting is in said second position for demanding.
 19. The ClO₂generator of claim 18, wherein said oxidant bound ion exchange mediumcomprises a tribromide bound ion exchange medium.
 20. A method ofgenerating ClO₂, comprising the steps of: providing a solid reagentbound medium in a first container having an inlet and an outlet withinsaid first container, a complementary reagent solution in a secondcontainer separate from said first container, coupled to said firstcontainer and upstream of said first container, a pressure sourcesituated upstream of said complementary reagent solution, and a firstvalve wherein said complementary reagent solution and said solid reagentbound medium are isolated from one another by said first valve when saidfirst valve is in a first position; switching said first valve to asecond position for forcing said complementary reagent solutiondownstream from said second container through said inlet and throughsaid reagent bound medium in said first container, wherein a ClO₂solution is generated in said first container; and discharging said ClO₂solution through said outlet from said first container upon placing asecond valve at said outlet of said first container in a position fordischarging.
 21. The method of claim 20, wherein said reagent boundmedium is an acidic ion exchange medium and said complementary reagentsolution is a chlorite solution.
 22. The method of claim 20, whereinsaid reagent bound medium is a chlorite bound ion exchange medium andsaid complementary reagent solution is an acid solution.
 23. The methodof claim 20, wherein said reagent bound medium is an oxidant bound ionexchange medium and said complementary reagent solution is a chloritesolution.
 24. The method of claim 20, wherein said reagent bound mediumis a chlorite bound ion exchange medium and said complementary reagentsolution is an oxidant solution.